Bladder function in female rats: effects of aging and pregnancy

In vivo anesthetized cystometrograms and in vitro bladder tissue strip responses were examined in three groups of female rats: young virgins (3 month), older virgins (8 month), and retired breeders (8-9 month). Significant age-related in vivo changes were observed including greater resting pressures, but smaller voided volumes, void durations and void-to-void intervals in older versus young virgin rats. There were significant age-related changes in the in vitro responses. Greater peak and steady state contractions to high K+-modified Krebs (80 mM) depolarization were observed in young animals compared to older animals. Plus, young virgins exhibited greater sensitivity but smaller maximal, normalized contractions to acetylcholine (ACh) than older virgins. Diminished responses to adenosine-5'-triphosphate (ATP) were detected in young versus older virgin rats. Pregnancy-related changes were compared between retired breeders and their age-matched controls, older virgin rats. In vivo voided volumes were greater in the retired breeders than in the older virgins. Smaller in vitro steady state contractions to high K+-modified Krebs depolarization and smaller normalized contractions to maximal concentrations of ACh were observed in the retired breeders than in the older virgins. Retired breeders exhibited diminished relaxation responses to norepinephrine compared to older virgins. ATP produced greater dose-dependent responses and greater maximal contractions in the retired breeders compared to the older virgins. In conclusion, age-related changes were present even prior to the onset of senescence, and multiple pregnancies altered bladder function.